In the coming year we plan to further investigate four areas: 1) Physiologic effects of aerosol size in asthma. We plan to expand our earlier observations that small particles are more effective and longer acting than larger particles by modification of the technique of aerosol inhalation. Specifically, we plan to investigate tidal volume versus vital capacity inhalation and the effect of breathholding. 2) Aerosol deposition in human lung. We plan to investigate the site of deposition of small and large particles utilizing technetium 99M and a scintillation camera. The technique(s) that will be compared will depend upon the final results of the physiologic studies. 3) Aerosol deposition in physical models (casts) of the human airway. The effects of hygroscopicity and humidity will be specifically investigated in the coming year. (4) Mathematical modelling of aerosol deposition in the human lung. We plan to compare physiologic data, and cast-model data, and the radioisotopic deposition data with our current mathematical description of hygroscopic particles. If there are significant deviations from the predictions the mathematical models will be critically reviewed and, if appropriate, changed.